1. Field of the Invention
The present invention relates to the cooling of components exposed to hot gas atmosphere and, more particularly, pertains to internally convectively cooled airfoil structures.
2. Description of the Prior Art
It is well known to cool airfoil structures, such as gas turbine blades or vanes, exposed to a hot gas atmosphere by circulating a cooling fluid through internal cooling passages defined within the airfoil structures in order to reduce the level of thermal stresses and reduce the peak airfoil temperatures in the airfoil structures and, thus, preserve the structural integrity and the service life thereof.
In gas turbine applications, the airfoil structures are typically air cooled by a portion of the pressurized air emanating from a compressor of the gas turbine engine. In order to preserve the overall gas turbine engine efficiency, it is desirable to use as little of pressurized air as possible to cool the airfoil structures. Accordingly, efforts have been made to efficiently use the cooling air. For instance, GB laid-open Patent Application No. 2,112,467 filed on Dec. 3, 1981 in the names of Schwarzmann et al. discloses a coolable airfoil having a leading edge cooling passage in which a plurality of identical and uniform sized trip strips are oriented at an angle to a longitudinal axis of the cooling passage in order to increase turbulence in the leading edge region of the blade, which is typically the most thermally solicited portion of the airfoil.
U.S. Pat. No. 4,416,585 issued on Nov. 22, 1983 to Abdel-Messeh and U.S. Pat. No. 4,514,144 issued on Apr. 30, 1985 to Lee both disclose a cooled blade having an internal cooling passage in which pairs of uniform sized ribs are angularly disposed to form a channel therebetween for channeling the cooling fluid along a selected flow path in order to increase heat transfer coefficient while at the same time minimizing the cooling fluid pressure drop in the internal cooling passage.
Although the heat transfer promotion structures described in the above-mentioned references are effective, it has been found that there is a need for a new and improved heat transfer promotion structure which allows for variable coolant flow and heat transfer coefficient distribution which can be set in accordance with a non-uniform external heat load.
It is therefore an aim of the present invention to provide a new and improved heat transfer promotion structure which is adapted to efficiently use cooling fluid to convectively cool a gas turbine airfoil structure.
It is also an aim of the present invention to provide such a heat transfer promotion structure which allows for variable cooling flow and heat transfer coefficient distributions.
Therefore, in accordance with the present invention there is provided a coolable gas turbine airfoil structure having a leading edge, a leading edge internal cooling passage through which a cooling fluid is circulated to convectively cool the airfoil structure, and a heat transfer promotion structure provided within the leading edge internal cooling passage. The heat transfer promotion structure comprises a plurality of trip strips arranged to cause the cooling fluid to flow towards the leading edge in a pair of counter-rotating vortices, thereby promoting heat transfer at the leading edge.
In accordance with a further general aspect of the present invention, there is provided a cooled airfoil structure for a gas turbine engine, comprising first and second opposed side walls joined together at longitudinally extending leading and trailing edges, at least one longitudinally extending internal cooling passage for passing a cooling fluid therethrough to convectively cool the airfoil structure, and a heat transfer promotion structure provided within the internal cooling passage. The heat transfer promotion structure includes a plurality of trip strips arranged inside the internal cooling passage to effect a variable heat transfer coefficient distribution. Each of the trip strips has a height (h) and a width (w) defining a w/h ratio. Within the plurality of trip strips, at least one of the height (h), the width (w) and the w/h ratio is varied along a transversal axis relative to the internal cooling passage. This advantageously provides variable flow and heat transfer coefficient distribution, thereby allowing to reduce cooling flow requirements.
In accordance with a further general aspect of the present invention, there is provided a method of cooling a leading edge of a gas turbine engine airfoil having a leading edge internal cooling passage extending between first and second side walls, comprising the steps of: providing a heat transfer promotion structure within the leading edge internal cooling passage, directing a cooling fluid into the leading edge internal cooling passage, and causing said cooling fluid to flow towards the leading edge in a pair of counter-rotating vortices, thereby promoting heat transfer at the leading edge.